The present invention relates to a head for injecting an ink as a pixel to a printing surface to form an image in an image printing apparatus for expressing gradation of a pixel as a minimum unit constituting an image in accordance with a change in recording area or printing density.
A printing image is constituted by a set of pixels as the minimum units of the image. An image printing apparatus capable of recording an image on the basis of image information of each pixel has been developed. In an image printing apparatus of this type, gradation of each pixel is expressed by changing a printing area of pixels or their printing density.
A conventional image printing apparatus of this type comprises an actuator controller arranged near an original image surface and a spray gun serving as a head electrically connected to the actuator controller through a solenoid valve. The spray gun is operated while the original image and paper are synchronously moved. An ink in an ink tank is guided through a flow path and sprayed from a nozzle to a paper surface by a siphon effect generated by an air pressure whose flow rate is controlled by the solenoid valve. At this time, the actuator controller outputs image information in units of pixels of the original image and ON/OFF-controls the solenoid valve. The ink is intermittently sprayed from the spray gun, and an image having gradation corresponding to the image information of the original image is printed on the printing surface.
Since the head in the conventional image printing apparatus comprises a siphon type spray gun having the solenoid valve, as described above, the apparatus as a whole including the valve body becomes heavy and is difficult to handle. In addition, since this apparatus employs the valve structure, response is poor. Since an amount of ink is controlled by air as a compressed fluid, the response time is further prolonged, and reproducibility of image information is degraded. Adjustment and maintenance operations are cumbersome and time-consuming, and much labor and skills are required due to the above reasons.